Final answer:
Internal nodes on a phylogenetic tree represent ancestors and branch points where two lineages diverge.
Step-by-step explanation:
In a phylogenetic tree, the internal nodes represent ancestors and are points in evolution when, based on scientific evidence, an ancestor is thought to have diverged to form two new species. These nodes are also known as branch points, where two lineages diverge. When two lineages stem from the same branch point, they are called sister taxa.